Development of Limit States Design Method for Joints with Dowel … pt3 .pdf · 2018. 8. 2. · Development of Limit States Design Method for Joints with Dowel Type Fasteners Basis

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Development of Limit States

Design Method for Joints with

Dowel Type Fasteners

Part 3: Basis of European

Yield Model Design Procedure

© 2004 Forest & Wood Products Research & Development Corporation All rights reserved. Publication: Development of Limit States Design Method for Timber Joints with Dowel Type Fasteners Part 3 Basis of EYM Design Procedure for Joints with Dowel-type Fasteners The Forest and Wood Products Research and Development Corporation (“FWPRDC”) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPRDC and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information. This work is copyright and protected under the Copyright Act 1968 (Cth). All material except the FWPRDC logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest and Wood Products Research and Development Corporation) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of the Forest and Wood Products Research and Development Corporation. Project no: PN02.1908 (Part 3) Researchers:

G.C. Foliente, M.J. Syme, I. Smith and M.N. Nguyen CSIRO Building, Construction and Engineering PO Box 56, Highett, Victoria 3190 Forest and Wood Products Research and Development Corporation PO Box 69, World Trade Centre, Victoria 8005 Phone: 03 9614 7544 Fax: 03 9614 6822 Email: [email protected] Web: www.fwprdc.org.au

Development of Limit States Design Method for Joints with Dowel Type Fasteners

Basis of European Yield Model Design Procedure

Prepared for the

Forest & Wood Products Research & Development Corporation

by

G.C. Foliente, M.J. Syme, I. Smith, M.N. Nguyen

The FWPRDC is jointly funded by the Australian forest and wood products industry and the Australian Government.

3

Contents

EXECUTIVE SUMMARY 4

1. INTRODUCTION 6

2. MODEL SELECTION 8

3. DETERMINING COMPONENT CAPACITIES 16

3.1 Timber Embedment Strength sH 16

3.2 Fastener Yield Moment MY 20

3.2.1 Characteristic yield moment 20

3.2.2 Validation of the conversion of tension test results to the yield moment 26

4. CALIBRATION/VALIDATION OF SIMPLIFIED EQUATIONS AND

COMPONENT CAPACITIES 28

4.1 Measured Yield Load from the Joint Tests 28

4.2 Calculated Yield Load by EYM Equations 29

4.3 Calibration 31

5. CONCLUDING REMARKS 48

REFERENCES 49

APPENDIX A. EUROPEAN YIELD MODEL 51

APPENDIX B. NOTATIONS 55

4

Executive Summary The current design procedure and design values for timber joints with dowel-type fasteners in

AS 1720.1 have been based on empirical fit of limited Australian joint test data, and the

procedures to determine design values were neither consistent nor fully understood. This

means that application of current design values to new products and materials used in timber

construction may not be appropriate, and that different safety factors (or levels of reliability)

may be obtained from different timber joints in current design (without the intention of the

designer).

The aim of this project was to develop a new strength limit states design procedure for timber

joints fabricated using Australian pine and dowel-type fasteners that address the limitations

of the current joint design procedure and design values in AS 1720.1. The project produced

four reports:

• BCE Doc 00/039 �Development of Limit States Design Method for Timber Joints � 1.

Literature review� (Foliente and Smith. 2000)


Comparison of experimental results with EYM predictions� (Smith et al. 2000)


Basis of EYM Design Procedure for Joints with Dowel-type Fasteners� (Foliente et al.

2002) (This report.)

• BCE Doc 01/081 Proposed Limit States Design Procedure for Timber Joints with

Dowel-Type Fasteners and Australian Pine (Foliente et al. 2002)

The current report (Part 3) presents the background details and related technical information

behind the proposed design procedures outlined in BCE Doc 01/081.

The new design procedures are based on the widely accepted European Yield Model (EYM),

providing both consistency and flexibility for the design of joints with dowel-type fasteners.

Timber design codes in the US, Canada and Europe all base the design of joints with dowel-

type fasteners on Johansen�s yield model (Johansen 1949, Larsen 1979). Known in North

America as EYM, this mechanics-based model presumes both the fastener and the wood

foundation upon which it bears behave as ideal rigid plastic materials. Deformation of joints is

not covered by this design procedure.

5

Tests used to validate the application of the EYM approach and a database of material

properties including the timber embedment strength and the yield moment of fasteners for

the EYM equations are summarised. A detailed description is given regarding the

determination of the component design values for use in the design procedure outlined in

BCE Doc 01/081.

A procedure for determination of the yield load from test data is described. These whole joint

test results are employed to calibrate the EYM prediction. The calibration is made via the

coefficients in the equation of the embedment strength. These coefficients were originally

fitted from embedded test data using transformed linear regression fit and analysis of

prediction errors. They were then calibrated so that the EYM predicted yield loads for the

joints are in good agreement with the measured yield load from the joint tests. Comparisons

with nominal joint capacities from the current timber design code AS 1720.1 are also made.

The new design procedures address the limitations of the current code. It has the following

features:

• It is based on a comprehensive experimental testing program with matched

specimens for joint testing and component/material testing (i.e., embedment strength

and fastener strength).

• The EYM-based equations of Whale et al. (1987) were selected based on a

comprehensive investigation of various EYM-based equations and comparison with

experimental data.

• The equations have been carefully calibrated to Australian test data, obtained from a

wide range of joint configuration.

• The proposed design method allows the use of new components/materials (i.e., not

limited to just those tested for AS 1720.1) as long as appropriate properties are

known or can be obtained by testing.

• The equations can be used for a variety of materials in the one joint, instead of

assuming the lowest capacity for all components within a joint.

• The bases for determining component/material properties and establishing the design

values of joint with dowel-type fasteners are consistent and well documented.

When implemented, the proposed design procedure would place Australian timber joint

design at par with world�s best practice.

6

1 Introduction

The current joint design procedure and design values in AS 1720.1 �Timber Structures, Part

1: Design methods� (SAA 1997) have two primary limitations: (1) they were based on early

American tests which were subsequently revised using an empirical fit of limited Australian

test data obtained between 1940 and mid-1970; and (2) the controlling criteria then in use to

determine design values are not fully known (i.e., are they related to strength or

deformation?) and the load factors vary considerably from one connector type to another for

no obvious reasons (Foliente and Leicester 1996). Because of the first limitation, the

applicability of current AS 1720.1 joint design values to new products or materials may be

questionable. In the last couple of decades, there has been a shift in the timber used in

house framing in Australia (from use of unseasoned to seasoned timber, and from

predominantly hardwood to predominantly softwood timbers). There has also been

introduction of a wider variety of fasteners, new sheathing panels and composite timber

products that are not explicitly addressed by the design standard. By default, whether

appropriate or not, the existing provisions and design values in AS1720.1 are often used for

these new products. Because of the second limitation, it is likely that different safety factors

(or levels of reliability) are obtained for different types of timber joints in current design

(without the intention of the designer).

The aim of this project was to develop a new strength limit states design procedure for timber

joints fabricated using Australian pine and dowel-type fasteners that addresses the

limitations of the current joint design procedure and design values in AS 1720.1. Part 1

reviewed the current design practice in Australia, USA, Canada and Europe, and identified

issues and experimental parameters that needed to be considered in order to apply the so-

called European Yield Model (EYM) for joints with dowel-type fasteners (Foliente and Smith

2000). Based on that literature review and results of a Connector Survey conducted by the

then Pine Research Institute (PRI), currently Plantation Timber Research (PTR), an

experimental test program was developed which:

1. Validated the applicability of the EYM equations in design of timber joints with Australian

Pine species; and

2. Established a database of material properties needed to use EYM-based design

equations for joints.

7

The positioning of these objectives in the overall logic for developing a new Australian design

procedure is shown in Fig. 1.1, encircled items 1 and 2.

The Part 2 report (Smith et al. 2000) presented details of the experimental program that

included tests on complete joints, embedment specimens and fasteners, and compared

experimental results with predictions from EYM-based equations. Alternative predictions

were considered based on the EYM equations and derivatives (see Appendix A) as follows:

• Johansen (1949) (referred to as �Original EYM�)

• Whale et al. (1987) (referred to as �Simplified-1�)

• Blass et al. (1999) (referred to as �Simplified-2�), and;

• US National Design Specifications (NDS) for wood construction (AF&PA 1997; 1999) for

wood and coach screws only (referred to as �NDS-Screw�).

Recommendations were made for the next phase of work that encompassed model

simplification, and development of design values and procedures (see Fig. 1.1 encircled

items 3, 4 and 5). These recommendations included adoption of the Whale et al. (Simplified-

1) EYM equations as the most appropriate for the development of a set of code rules for

design of timber joints with dowel-type fasteners and Australian pine.

An accompanying document, CSIRO BCE Doc 01/081 (Foliente et al. 2002), details the set

of code rules developed as part of the third stage of this project. The current report (Part 3)

presents the basis of the design procedure outlined in CSIRO BCE Doc 01/081.

Figure 1.1 Overall logic

of joint design

development

DERIVATION OFCHARACTERISTICPROPERTIES

MATERIAL PROPERTIES� Embedment strength� Nail yield moment

EUROPEAN YIELDMODEL

MODELSIMPLIFICATION

VERIFICATIONTESTS

CODE RULESAND LANGUAGE

1

2

3

4

5

8

2 Model Selection

The equations of the original EYM model and its derivatives are presented in Appendix A.

The Whale et al. (Simplified-1) EYM equations from the Part 2 report (Smith et al 2000) were

chosen for the following reasons:

• Whilst all the EYM-type models considered in Part 2 of the project produced

conservative estimates of the joints� ultimate capacity, the Blass et al. (Simplified-2)

model was in some instances highly conservative. This occurred when one of the two

�interpolation� equations governed. Although the Blass et al.�s equations were the

simplest set among the models considered, for some cases their conservative results

are difficult to justify.

• The NDS Screw equations did not produce predictions very different to those obtained

using the Johansen (Original) or Whale et al. (Simplified-1) equations. The NDS Screw

equations are the most complex and gave conservative results.

• The Johansen (Original) and Whale et al. (Simplified-1) EYM equations produced similar

predictions for all the joints tested in Part 2 of the project. As calculations are more

streamlined using the Whale et al. equations, it seemed appropriate to choose those

equations for the recommended design procedure. This mirrors current practice in

Canada.

Figures 2.1 to 2.4 show the predictions of the various EYM equations using average values

of embedment strength sH and yield moment MY, in relationship to the experimental data.

Note that the EYM equations predict joint �yield� load and not ultimate load capacity.

9

Legend: Predicted Capacity Original EYM Simplified-1 Simplified-2

C

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6

Displa cement (mm)

Load

(N)

Nail N4 A

B

(a)

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14

Displacement (mm)

Load

(N)

Nail N10 A

B

A

B

(b)

Figure 2.1 Nailed joints � Comparing experimental data to predictions:

(a) N4 is a 2-nail joint of 35mm-thick Radiata pine members, and 3.05φ x 75mm long nails.

(b) N10 is a 1-nail joint of 45mm-thick Radiata pine members, and a 3.05φ x 75mm long nail.

10

Legend: Predicted Capacity Original EYM Simplified-1 Simplified-2 NDS-Screw

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 2 4 6 8 10

Displacement (mm)

Load

(N)

Screw S2 A

B

(a)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 10 20 30 40 50

Displaceme nt (mm)

Load

(N)

Screw S3 A

B

(b)

Figure 2.2 Type 17 screw joints � Comparing experimental data to predictions: (a) S2 is a 1-screw joint of (A) 18mm and (B) 35mm thick Radiata pine members,

and a No. 8 x 40mm long type-17 screw with shank φ = 3.4mm. (b) S3 is a 1-screw joint of (A) 65mm and (B) 44mm thick Radiata pine members,

and a No. 14 x 115mm long type-17 screw with shank φ = 5.2mm.

11


0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10 12 14

Displaceme nt (mm)

Load

(N)

Coach Screw CS1 A

B

(a)

0

1000

2000

3000

4000

5000

6000

7000

0 5 10 15 20

Displacement (mm)

Load

(N)

Coach Screw CS2S A

B

(b)

Figure 2.3 Coach screw joints � Comparing experimental data to predictions: (a) CS1 is a 2-coach screw joint of (A) 20mm and (B) 45mm thick Radiata pine members,

and 6φ x 65mm long coach screw. (b) CS2S is a 1-coach screw joint of (A) 20mm and (B) 45mm thick Slash pine members,

and 6φ x 65mm long coach screw.

12


0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25 30

Displaceme nt (mm)

Load

(N)

Bolt BSS1 A

B

(a)

0

2000

4000

6000

8000

10000

12000

14000

16000

0 2 4 6 8 10 12 14

Displaceme nt (mm)

Load

(N)

Bolt BDS1 B

A C

(b)

Figure 2.4 Bolted joints � Comparing experimental data to predictions: (a) BSS1 is a 1-bolt single shear joint of two 35mm thick Radiata pine members, and an

8φ x 90mm long bolt. (b) BDS1 is a 1-bolt double shear joint of three Radiata pine members:(A) 35mm,

(B) 45mm, (C) 35mm thick, and an 8φ x 130mm long bolt.

13

The yield modes for two-member joints and three-member joints are shown in Figures 2.5

and 2.6, respectively. Modes I and II correspond to timber bearing failures and modes III and

IV to plastic hinge formation in the fastener. Subscript �s� means side member yielding, and

�m� means main member yielding. The characteristic capacity of a joint interface, Qki, for each

yield mode is given by the Whale et al. (Simplified-1) EYM equations, as shown below:

2-Member joints

( )

+

++

++

+

=

IV 1

4

III 5)1(

III 2.0)1(

II 5

1I I 0.1

min2

m2

s2

m

s

ββ

αββ

ββ

αβαβ

dlsM

dlsM

dlsM

dlsQ

H

Y

H

Y

H

Y

Hki (2.1)

3-Member Symmetric joints

( )

s

m

2

2

1.0 I0.5 I

0.2 III(1 )

4 IV1

min

Yki H

H

Y

H

MQ s dl s dl

Ms dl

αβ

ββ

ββ

+= +

+

(2.2)

where terms are defined, with reference to Figures 2.7 and 2.8, as follows:

sH = characteristic embedment strength of the side member (in a 3-member joint, use

the minimum side member sH). d = diameter of fastener (shank diameter in the case of threaded fasteners)

l = side member thickness as defined in Figure 2.7 for a 2-member joint and in

Figure 2.8 for a 3-member joint.

� = ratio of the penetration into the main member to the thickness of the side member

for a 2-member joint, and as defined in Figure 2.8 for a 3-member joint.

� = ratio of sH of the main member to sH of the side member (in a 3-member joint, use

maximum side member sH)

14

MY = characteristic yield moment of fastener as determined by bending tests or as

calculated from tension test results.

Mode IVMode IIIMode IIMode I

[ plastic hinge ]

Figure 2.5 Yield modes for two-member joints

Mode IVMode III Mode ImMode Is

[ plastic hinge ] Figure 2.6 Yield modes for three-member joints

15

Figure 2.7 Illustration of 2-member joint definitions

Figure 2.8 Illustration of 3-member joint definitions

(b) Bolted joint

d

(a) Nailed or screwed joint

d

main member

l

side member side member

main member

l

α = lm / max [ l1, min( l2, l3)]

(a) Nailed or screwed joint

main memberd

side members

l1 lm l3

l = min ( l1, l2, l3 )

l2

(b) Bolted joint

d

side members

l1 lm l2

l = min ( l1, l2 )

α = lm / max ( l1, l2 )

16

3 Determining Component Capacities

3.1 Timber Embedment Strength sH

In order to estimate the embedment strength of a timber component within a joint, a

prediction equation was sought. Based on earlier work (Whale and Smith 1989) the form of

the embedment strength equation was assumed to be

b caHs dρ= (MPa) (3.1)

where

ρ = density of wood (kg/m3)

d = shank diameter of fastener (mm)

a, b, and c are curve fitting coefficients.

A regression analysis was performed in order to determine coefficients a, b and c using all

individual test replicate data for sH and ρ for the regression equation log sH = a + b logρ +

c logd. The average diameter for each set of embedment test replicates was calculated and

assumed for d. Axum Version 6.0 (MathSoft, 1999) � a software for data analysis - was used

to perform the regression analysis.

Figures 3.1a and 3.1b show the test set-up for obtaining the embedment strength.

17

Embedment specimen

Fastener

Dummy (reaction) end

Figure 3.1a Embedment test (schematic)

(a) (b) (c)

Figure 3.1b Embedment test apparatus and test arrangement: (a) apparatus for

testing small specimens (load parallel to grain) (b) apparatus for testing large specimens (load parallel to grain) (c) apparatus for testing large specimens (load perpendicular to grain)

18

Figure 3.2 Definition of embedment strength

Figure 3.2 illustrates the method used for determining embedment strength. This procedure

was used to obtain the basic trend for nails, screws, coach screws, bolts loaded parallel to

grain (hereafter called �bolts parallel�) and bolts loaded perpendicular to grain (hereafter

called �bolts perpendicular�). The regression analyses determine the mean coefficients am,

bm and cm, which are used with mean values of ρ and d to determine a mean value for sH.

The results of this analysis are in Table 3.1.

Table 3.1 Results of regression analysis showing the mean coefficients giving the basic

trend.

Coefficient Fastener type

am bm cm

Nails 0.0176 1.27 -0.143

Screws 0.111 1.15 -0.935

Coach screws 0.165 0.941 -0.319

Bolts parallel 0.0965 0.996 -0.106

Bolts perpendicular 1.98 0.575 -0.429

Embedment

Bearing Stress

Embedment Strength

19

The goodness of the fit was evaluated by analysing the prediction error. The prediction error

was defined as follows:

100predicted testedprediction errortested

− = ×

(%) (3.2)

The predicted sH by Eq (3.1) with the coefficients listed in Table 3.1 were compared to the

average tested sH values for each type of fasteners. The results, including the average, the

standard deviation, the maximum and the minimum values of the prediction errors for each

type of fastener are shown in Table 3.2.

Table 3.2 Results of the analysis of prediction error

Prediction error (%) Fastener type

Average Standard

Deviation Maximum Minimum

Nails -0.4 8.8 14.1 -13.4

Screws 4.2 13.7 18.9 -15.4

Coach screws -2.0 15.5 23.3 -16.5

Bolts parallel -1.6 11.7 27.0 -14.8

Bolts perpendicular -4.9 13.9 16.7 -16.8

An ideal fit would give an average prediction error of ±2%, minimum and maximum error

within ±15% with 90% of prediction within ±10%. The results shown in Table 3.2 are not

unreasonable � considering the range of differences in the joint system, detailed nature of

joint action and predominant failure modes - and for practical design purposes would be

acceptable (note that the design values are eventually taken from the lower 5th percentile

range).

When observing the results of embedment strength calculations for bolts shown in Tables B5

and B6 of the accompanying document, CSIRO BCE Doc. 01/081 (Foliente et al, 2002), it is

interesting to compare bolts parallel with bolts perpendicular to grain. For the larger diameter

fasteners, the embedment strengths for bolts perpendicular are significantly less than for

bolts parallel to grain. This difference reduces as the fastener diameter reduces. In one

case (8 mm diameter, JD5), the embedment strength of the bolt perpendicular is greater than

that for the bolt parallel. With reference to the embedment strength tests given in Smith et al,

20

2000, the ratio of the average values of embedment strength perpendicular to embedment

strength parallel decrease with increasing bolt diameter as shown in Figure 3.3 below.

00.20.40.60.8

1

0 5 10 15 20 25

Bolt diam. (mm)

Rat

io o

f Ave

. Em

bed.

St

reng

th P

erp/

Para

llel

Figure 3.3 Effect of bolt diameter on the ratio between embedment strengths observed when

loaded perpendicular and parallel to grain

When characteristic values were subsequently calculated (a procedure that takes into

account variability in test data), this effect was further compounded to the point where the 8

mm diameter, JD5 embedment strength perpendicular was greater than the parallel

embedment strength.

Embedment test data from the testing reported (Smith et al. 2000) showed that generally the

embedment strength when the thread is bearing against the timber is slightly higher than

when the shank of the fastener is bearing against the timber. The embedment strength in

this case was calculated assuming the shank diameter for the bearing area for both the

thread bearing and shank bearing on the timber. It is therefore slightly conservative to

assume that the embedment strength for the threaded portion of the fastener is the same as

for the shank portion.

21

3.2 Fastener Yield Moment MY

3.2.1 Characteristic Yield Moment

The average MY for each set of bending test replicates was calculated. The characteristic

value for MY was taken as the 5th percentile value of the test results calculated assuming a

normal distribution. The 5th percentile of the yield moment, MY,0.05, was calculated as

MY,0.05 = MY,mean (1 − 1.645 V) (3.3)

where MY,mean is the average MY for each set of bending test replicates; V is the assumed

coefficient of variation, taken as 0.08 based on the average coefficient of variation observed

in the MY test results for all fasteners (Smith et al. 2000).

Figures 3.4 and 3.5 show the test set-up for obtaining the yield moment. Figure 3.6 illustrates

the method for determining yield moment.

Figure 3.4 Principle of bending apparatus for small diameter fasteners

Reaction Point

Lever arm

F

L

l2

M = FL

22

Figure 3.5 Bending apparatus for small diameter (d ≤ 8mm) fasteners

23

Rotation reaction point (deg.)

Nail bending moment

Yield Moment

0.0

Figure 3.6 Interpretation of moment-rotation plots for small diameter (d ≤ 8mm) fasteners

In the case of fasteners that were too large (d > 8mm) to fit into the CSIRO bending test rig,

tension tests according to AS/NZS 4291.1 (SAA 1995) were carried out and the yield

moment calculated using the following formula (Whale and Smith 1987, Ehlbeck and Larsen

1993)

MY = (σy + σult ) dshank3 / 12 (3.4)

where σy is the yield stress, σult is the ultimate stress and dshank is the diameter in the shank

(unthreaded portion) of the fastener.

Based on previous studies (AF&PA 1999) and checks with the configuration of Australian

bolts (SAA/SNZ, 1996a) and type-17 screws (SAA 2002), MY for the threaded portion was

assumed to be 0.75 times the calculated value for the shank of bolts and type-17 screws.

Given the relatively tight tolerances on the minimum thread diameter of bolts and type-17

screws in the standards, the factor of 0.75 should be adequate for fasteners produced in

accordance with those standards.

For coach screws, MY for the threaded portion of the fastener was assumed to be 0.5 times

the calculated value for the shank. This assumption was based on the average geometry of

coach screws used in the CSIRO test program (Smith et al. 2000). But it should be noted

that the minimum thread diameter of those coach screws was greater than the minimum

allowed according to SAA/SNZ (1996b). It is therefore possible that coach screws may be

produced in accordance with the Standard that have a threaded portion MY value less than

24

that given in the proposed design procedure. Due to the broad tolerances for the minimum

thread diameter in the standard, the properties of the coach screws that are used in Australia

construction should be monitored to ensure that minimum thread diameters are not

significantly less than those observed during the CSIRO tests.

Figure 3.7 shows tension test specimens for the bolts and coach screws that were too large

to fit in to the bending test rig. Figure 3.8 depicts the yield and ultimate stress levels used in

Eq. (3.4) to determine yield moment.

25

Figure 3.7 Typical tension test specimens for large bolts, and large coach screws (d > 8mm)

Cross-head movement

Axial Stress

Yield stress, σY

Ultimate stress, σult

Figure 3.8 Interpretation of tension test data for large bolts and large coach screws

26

3.2.2 Validation of the conversion of tension test results to the yield moment

The approach used to validate the conversion of tension test results to MY values in Eq. (3.4)

was to compare MY values obtained by tension tests to those obtained by bending test.

Bending tests on a range of Australian produced bolts and coach bolts were performed at the

University of Karlsruhe, Germany on their bending test machine. The University of Karlsruhe

bending test machine was similar to the one constructed and used at CSIRO but had the

capacity to test fasteners up to 20 mm in diameter.

Four types of Australian fasteners, including coach screws with nominal diameters of 20 and

12mm, and bolts with nominal diameters of 20 and 16mm were tested by the bending test

machine at the University of Karlsruhe. The number of replicates for each type of fastener

was 3. The measured yield moments were then averaged to give the MY result for each type

of the fasteners.

In a parallel experiment, tension tests of the same types of fasteners were carried out at

CSIRO. The number of replicates for each type of fastener was also 3. Yield loads were

calculated by Eq. (3.4) and then averaged over the 3 replicates for each type of fastener.

Table 3.3 provides the comparison of the average MY results for the bolts and coach screws

tested from the bending test apparatus at University of Karlsruhe with those calculated from

tension tests� results at CSIRO. The % difference was calculated as:

100calculated testedDifferencetested

− = ×

(%) (3.5)

On average, the yield moments MY from Karlsruhe�s bending tests are about 20% higher

than those calculated from tension tests. It is noted that the thread of the fastener was

subjected to bending in the Karlsruhe bending tests, so the minor diameter of the thread was

used in the calculation of MY by Eq.(3.4). This would underestimate MY because the stress

area of thread (which should be used to calculate MY) is greater than minor thread diameter

area. The stress area of the threads for the tested fasteners was not readily available.

27

Table 3.3 Comparison of average MY results derived from bending test with those derived

from tension tests.

Fastener type

Nominal

diameter

(mm)

MY calculated

from tension

tests at CSIRO

(Nmm)

MY tested from

Karlsruhe�s

bending test

(Nmm)

Difference

(%)

20 238509 317000 24 Coach Screw

12 64614 70000 8

20 507747 657250 23 Bolt

16 222304 283600 22

The bolts tested in tension were machined quite significantly to reduce the cross-section as

required for testing according to AS/NZS4291.1 (SAA 1995). A possible reason for the

discrepancy is the removal of hardened outer layers of steel in large diameter bolts. As those

are the layers that would do most work in bending, the negative effect on strength could be

significant. Although this would seem to fit with the diameter dependence of the error,

whether it is a correct explanation depends on how the bolts were actually manufactured.

A check on the accuracy of the CSIRO bending test apparatus for small diameter fasteners

was also undertaken by comparing test results from the CSIRO bending test apparatus with

those obtained from the University of Karlsruhe bending test apparatus for 8 mm bolts.

Number of the test replicates was 5. The average MY values for an 8 mm diameter bolt

measured in the CSIRO and University of Karlsruhe bending test apparatus were

33928 Nmm and 35080 Nmm, respectively, which were only 3% different from each other.

This very small difference proved the accuracy of the CSIRO bending test apparatus.

In summary, it is concluded that for large diameter fasteners (d > 8mm), the tension test

procedure and the conversion equation in Eq.(3.4) provide a simple and effective method to

estimate their yield moment. And for small diameter fasteners (d ≤ 8mm), yield moment can

be obtained directly using the CSIRO bending test apparatus.

28

4. Calibration/Validation of Simplified Equations and Component Capacities

4.1 Measured Yield Load from the Joint Tests

The experimental program in the Part 2 Report (Smith et al. 2000) included a total of 360

complete joint system tests with materials matched with those used in the component tests

described in the previous Section. The ultimate load Pu and yield load Py for all individual

joints were determined. From the load-displacement plot of each joint, they were obtained as

follows:

• The ultimate load, Pu, is taken as the maximum load.

• The yield load, Py, is taken as the load co-ordinate at the intersection of a tangent

representing maximum slope within the initial slip region, and a tangent representing the

stabilised slope region of the load-slip curve that follows the first onset of reduced

stiffness (Figure 4.1). Any irregularities in the load-slip curve close to when load equals

zero are neglected while fitting the tangent in the initial slip region. It is possible for the

load-slip curve to recover stiffness after the region of stabilised slope. However, that is

due to gap closure, friction and string effects and is not reflective of the yield point which

normally will be the load level at which a plastic hinge(s) forms in the fastener(s). The

length of the stabilised region can be quite small but this does not mean that it should be

discounted. Figure 4.1 shows four examples of application/implementation of this

procedure for different types of load-displacement plots.

Normalised characteristic loads Pu,norm and Py,norm were calculated for each set of joint test

replicates, using the following equations:

0.052.71k

VP Pn

= −

(4.1)

( )0.85 0.95 / 0.8norm kP V P= − (4.2)

where P0.05 is the fifth percentile value of measured data, Pk is characteristic load, n is

number of joint test replicates, and V is the coefficient of variation of the measured data.

These equations are recognised in engineering statistics and are consistent with equations

29

proposed for the draft of the Australian/New Zealand Standard for timber connections

�Methods for evaluation of mechanical joint systems� (SAA 1998, Bryant and Hunt 1999).

The nominal capacities (i.e. without application of capacity reduction factor φ) for each joint

test configuration were also calculated in accordance with AS 1720.1 (SAA, 1997) for

reference.

Figure 4.1 Determination of Yield Load for 4 different types of load-displacement curves

P

δ

P

δ

P

δ

P

δ

Py

Py

Py

Py

P

δ

P

δ

P

δ

P

δ

Py

Py

Py

Py

30

4.2 Calculated Yield Load by the EYM Equations

The group fifth percentile density �0.05 for each set of test replicates was used for the

calculation. It is assumed that:

• The densities are normally distributed.

• The coefficient of variation (V ) is 10%, based on the coefficients of variation of the

density of wood members in the embedment tests (Smith et al. 2000).

• The mean density �mean is equal to the minimum group mean density from Table 1 of

AS 1649 (SAA 2001).

With these assumptions, the fifth-percentile density�0.05 can be computed as

�0.05 = �mean (1 � 1.645 V) (4.3)

The fifth-percentile densities for JD3, JD4, and JD5 joint groups are determined in Table 4.1.

The average diameter of the fasteners was calculated for each set of joint test replicates and

taken as d.

Table 4.1 Determination of the fifth percentile density for joint groups

Joint group

Group mean density

range (kg/m3)

(Table 1, AS1649)

Group mean density,

�mean (kg/m3)

Group fifth-percentile

density �0.05 (kg/m3)

JD3

JD4

JD5

600 to 745

480 to 595

380 to 475

600

480

380

500

400

320

The characteristic embedded strength sH was then calculated by Eq. (3.1), using the

coefficients am, bm, and cm listed in Table 3.1, and the group fifth percentile density �0.05 and

the average diameter d. Smith and Foliente (2001) have shown that it is appropriate to use

the characteristic sH to predict the characteristic joint strength.

The calculated characteristic yield load Py,EYM was then evaluated as the characteristic

capacity of a joint interface Qki in the EYM equations (2.1) and (2.2), using the characteristic

sH as computed above and the characteristic MY derived in Section 3.2 for each joint test

configuration.

31

4.3 Calibration

The characteristic yield loads Py,norm determined from the actual joint tests as in Section 4.1

were compared with the calculated Py,EYM determined by EYM model as in Section 4.2.

Comparisons of the calculated Py,EYM with the nominal capacity determined by AS 1720.1

were also made for reference. These comparisons are shown on plots (a) and (b),

respectively, in Figures 4.2 to 4.6 for 5 different types of fasteners. In plots (a) of these

figures, the location of a point relative to the diagonal indicates if the calculated value is

conservative or not. The conservative region is above the diagonal, and the non-conservative

region is shaded under the diagonal. It can be seen that the calculated and the joint test�s

yield loads were in generally good agreement, but in some cases, minor calibrations may be

needed.

The calibration was made by first rounding and then adjusting (if necessary) the coefficients

am, bm, and cm to give joint-calibrated coefficients aj, bj, and cj to be used in Eq. (3.1). The

target of the calibration was to match the calculated Py,EYM to the joint test�s normalised

characteristic Py,norm (left plots in Figs 4.2 to 4.6). The calculated Py,EYM was also compared to

the AS 1720.1�s nominal capacities (right plots in Figs 4.2 to 4.6). The final results of the

calibrations for different joint configurations are shown in Tables 4.2 to 4.6 and plots (b) in

Figs. 4.2 to 4.6. The new joint-calibrated coefficients aj, bj and cj are listed in Table 4.7.

Some remarks on the calibration process are given below:

• In the calibration for nails, the coefficients were adjusted to bring the calculated Py,EYM

down to the joint test�s Py,norm values, tempered somewhat by the fact that the existing AS

1720.1 values were consistently well above both the Py,norm and Py,EYM values (except in

one case where the AS 1720.1�s value was 2% below the Py,norm value). The ratio of

Py,EYM to AS 1720.1�s nominal capacity was relatively consistent indicating that the

empirically based AS 1720.1 system gave similar trends to the mechanics based EYM

system. In order to be consistent with all dowel fastener types, the Py,EYM values had to

be brought back toward the joint test�s Py,norm values. The calibration result is in Table 4.2

and Figure 4.2(b).

• Calibration for the screw fasteners was less certain because of significant fluctuations of

test results about the EYM predictions and a relatively small sample size. Due to

dimensional considerations the first three screw test configurations could not strictly be

given an AS 1720.1 capacity (one was given, ignoring the rule nominating the joints as

32

non-load bearing). A slightly conservative calibration was given for the above reasons.

The calibration result is in Table 4.3 and Figure 4.3(b).

• The EYM prediction Py,EYM was calibrated to Py,norm for coach screws. The calibration

result is in Table 4.4 and Figure 4.4(b). Very small adjustments were made for this case.

• Comments regarding the calibration for nails apply similarly to the calibration for bolts

loaded parallel to grain. The calibration result is in Table 4.5 and Figure 4.5(b).

• The EYM prediction Py,EYM was calibrated to Py,norm for bolts loaded perpendicular to

grain. The calibration result is in Table 4.6 and Figure 4.6(b).

Tables 4.2 to 4.5 show the result of the calibration for each type of fastener. Each table

provides the calculated Py,EYM, the AS1720.1 nominal capacity and the normalised

characteristic loads Pu,norm and Py,norm of the joint tests for each set of the test replicates.

Comparisons between these values are then made in terms of their ratios to each other. The

comparisons are then summarised by computing the average, minimum and maximum of

these ratios. These values are considered during the calibration process, and the main target

is to bring the average of the ratio Py,EYM / Pynorm as close to 1 as possible. It is also noted

that for all types of fasteners except for the type-17 screw, the AS 1720.1 nominal capacity is

higher than the joint test Py,norm.

Figures 4.7 to 4.11 show the joint tests� load-displacement curves and their corresponding

calculated Py,EYM, nominal capacity from AS1720.1, and normalised characteristic yield load

Py,norm for some typical groups of joint configurations. It is seen that the calculated Py,EYM

values consistently provide reasonable estimates of the joints� yield load. AS 1720.1 can be

either overly conservative [as in Fig.4.8(a) for screw joint S1] or dangerously non-

conservative [as in Figs.4.9(b), 4.10(a) and (b) for coach screw joint CS3 and bolted joints

BSS1 and BDS3, respectively].

In summary, the set of slightly adjusted coefficients for sH calculation as presented in

Table 4.7 provides Py,EYM values that are, for practical design purposes, consistently good

enough compared to test data.

Thus, the final sH equations for calculation of Py,EYM are:

• For nails,

1.2 0.20.02Hs dρ −= (4.4)

33

• For Type 17 screws,

1.1 1.00.1Hs dρ −= (4.5)

• For coach screws,

0.9 0.30.2Hs dρ −= (4.6)

• For bolts parallel to grain,

0.20.1Hs dρ −= (4.7)

• For bolts perpendicular to grain,

0.6 0.51.9Hs dρ −= (4.8)

where

sH = characteristic embedment strength, in MPa

ρ = group 5th percentile air dry density of timber at 12 % moisture content (see

Table 4.1), in kg/m3

d = diameter of fastener (shank diameter in the case of threaded fasteners), in mm.

34

Table 4.2 Result of calibration for nail joints

Joint Tests Comparison Joint type

Fastener diameter d (mm)

Joint group

Calculated Py,EYM

AS 1720.1’s Nominal Capacity Py,norm Pu,norm Py,EYM /

Pynorm Py,EYM /

AS1720.1

Pynorm / AS1720

.1 N1 2.8 JD5 471 545 333 588 1.42 0.86 0.61 N2 2.8 JD4 542 665 358 558 1.51 0.81 0.54 N3 3.15 JD5 617 680 368 798 1.68 0.91 0.54 N4 3.05 JD5 589 641 652 940 0.90 0.92 1.02 N5 3.05 JD4 678 769 597 793 1.14 0.88 0.78

N4S 3.05 JD4 678 769 558 534 1.22 0.88 0.73 N5S 3.05 JD3 775 1076 637 890 1.22 0.72 0.59 N6 3.75 JD5 809 915 714 1210 1.13 0.88 0.78 N7 4.5 JD5 1056 1255 1163 1089 0.91 0.84 0.93 N8 3.15 JD5 617 680 476 585 1.30 0.91 0.70 N9 3.05 JD5 617 641 567 890 1.09 0.96 0.88

N10 3.05 JD4 678 769 660 929 1.03 0.88 0.86 Averag

e 1.21 0.87 0.75

Max 1.68 0.96 1.02

Min 0.90 0.72 0.54 Notes: • Tests N1 to N7 were performed using two nail joints. Values shown are reduced to single

nail values. • All joint tests were 2-member

35

Table 4.3 Result of calibration for type-17 screw joints



Joint group

Calculated Py,EYM


Pynorm Py,EYM /

AS 1720

Pynorm / AS1720

S1 3.40 JD5 482 361 (NLB) 444 492 1.08 1.33 1.23 S2 3.80 JD5 565 523 (NLB) 1641 2049 0.34 1.08 3.14

S2S 3.80 JD5 565 523 (NLB) 1013 1566 0.56 1.08 1.94 S2S

E 3.40 JD4 702 656 316 308 2.22 1.07 0.48 S3 5.20 JD4 1531 3103 1537 3583 1.00 0.49 0.50

Average 1.04 1.01 1.46

Max 2.22 1.33 3.14

Min 0.34 0.49 0.48 Notes: • �NLB� denotes that strict interpretation of AS 1720.1 would give this fastener configuration

as non-load bearing. • All joint tests were 2-member

Table 4.4 Result of calibration for coach screw joints



Joint group

Calculated Py,EYM


Pynorm Py,EYM /

AS1720.1

Pynorm / AS1720

.1 CS1 5.50 JD4 1614 2100 1784 1428 0.90 0.77 0.85 CS2 5.50 JD5 1401 1690 968 2796 1.45 0.83 0.57 CS2

S 5.50 JD4 1614 2100 1646 2711 0.98 0.77 0.78 CS3 11.50 JD4 5736 7400 4663 7203 1.23 0.78 0.63 CS4 18.70 JD4 12844 20400 8967 9850 1.43 0.63 0.44

Average 1.20 0.75 0.66

Max 1.45 0.83 0.85

Min 0.90 0.63 0.44 Notes: • Test CS1 was performed using a two-screw joint. Values shown are reduced to single

screw values. • All joint tests were 2-member

36

Table 4.5 Result of calibration for bolts joints with member loaded parallel to grain



Joint group

Calculated Py,EYM


Pynorm Py,EYM /

AS1720.1

Pynorm / AS1720

.1 BSS

1 7.00 JD4 2663 4350 2402 3636 1.11 0.61 0.55

BSS2 7.00 JD5 2108 3650 1582 4501 1.33 0.58 0.43

BSS2S 7.00 JD4 2663 4350 848 722 3.14 0.61 0.20

BDS1 7.00 JD5 5087 7800 5267 8550 0.97 0.65 0.68

BDS2 7.00 JD5 5087 7800 3717 6691 1.37 0.65 0.48

BDS3 14.75 JD5 12302 20200 15598 16263 0.79 0.61 0.77

BDS4 18.30 JD4 24621 42800 23011 20355 1.07 0.58 0.53

Average 1.40 0.61 0.52

Max 3.14 0.65 0.77

Min 0.79 0.58 0.20 Notes: • Splitting occurred in 5/10 joint tests for the BDS4 configuration • Splitting occurred in 9/10 joint tests for the BSS2S configuration

37

Table 4.6 Result of calibration for bolts joints with member loaded perpendicular to grain



Joint group

Calculated Py,EYM


Pynorm Py,EYM /

AS1720.1

Pynorm / AS1720

.1 BSS

3 14.75 JD5 3238 4900 5692 15492 0.57 0.66 1.16

BSS4 20.10 JD4 7455 15300 8356 15501 0.89 0.49 0.55

BDS5 7.03 JD4 5871 7000 3806 8095 1.54 0.84 0.54

BDS6 7.03 JD5 5311 5000 2994 6479 1.77 1.06 0.60

BDS6S 7.03 JD4 5871 7000 4946 6789 1.19 0.84 0.71

BDS7 14.75 JD5 10409 9800 14420 15838 0.72 1.06 1.47

BDS8 18.30 JD4 17785 30600 18447 33628 0.96 0.58 0.60

Average 1.09 0.79 0.80

Max 1.77 1.06 1.47

Min 0.57 0.49 0.54 Table 4.7 Final coefficients for sH calculation based on the calibration with joint test results

Coefficient Fastener type aj

(original am) bj

(original bm) cj

(original cm)

Nails 0.02

(0.0176)

1.2

(1.27)

-0.2

(-0.143)

Screws 0.1

(0.111)

1.1

(1.15)

-1.0

(-0.935)

Coach screws 0.2

(0.165)

0.9

(0.941)

-0.3

(-0.319)

Bolts parallel 0.1

(0.0965)

1.0

(0.996)

-0.2

(-0.106)

Bolts perpendicular 1.9

(1.98)

0.6

(0.575)

-0.5

(-0.429)

38

0

500

1000

1500

0 500 1000 1500

Calculated P y,EYM

AS 1

720.

1 no

min

al c

apac

ity

0

500

1000

1500

0 500 1000 1500

Calculated P y,EYM

Py,

norm

from

join

t tes

ts

conservative region

non-conservative region

(a) Calculated using original mean coefficients am, bm, and cm

0

500

1000

1500

0 500 1000 1500

Calculated P y,EYM

AS

1720

.1 n

omin

al c

apac

ity

0

500

1000

1500

0 500 1000 1500

Calculated P y,EYM

Py,

norm

from

join

t tes

ts

conservative region


(b) Calculated using joint-calibrated coefficients aj, bj, and cj Figure 4.2 Comparison of calculated Py,EYM by EYM model with Joint test�s Py,norm (left) and

with AS1720.1�s nominal capacities (right) for nail joints.

39

0

1000

2000

3000

4000

0 1000 2000 3000 4000

Calculated P y,EYM

AS 1

720.

1 no

min

al c

apac

ity

0

1000

2000

3000

4000

0 1000 2000 3000 4000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


0

1000

2000

3000

4000

0 1000 2000 3000 4000

Calculated P y,EYM

AS

1720

.1 n

omin

al c

apac

ity

0

1000

2000

3000

4000

0 1000 2000 3000 4000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


with AS1720.1�s nominal capacities (right) for type-17 screw joints.

40

0

10000

20000

30000

0 10000 20000 30000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region

0

10000

20000

30000

0 10000 20000 30000

Calculated P y,EYM

AS

172

0.1

nom

inal

cap

acity


0

10000

20000

30000

0 10000 20000 30000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region

0

10000

20000

30000

0 10000 20000 30000

Calculated P y,EYM

AS

172

0.1

nom

inal

cap

acity


with AS1720.1�s nominal capacities (right) for coach screw joints.

41

0

15000

30000

45000

0 15000 30000 45000

Calculated P y,EYM

AS 1

720.

1 no

min

al c

apac

ity

0

15000

30000

45000

0 15000 30000 45000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


0

15000

30000

45000

0 15000 30000 45000

Calculated P y,EYM

AS

1720

.1 n

omin

al c

apac

ity

0

15000

30000

45000

0 15000 30000 45000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


with AS1720.1�s nominal capacities (right) for bolts joints loaded parallel to grain.

42

0

10000

20000

30000

40000

0 10000 20000 30000 40000

Calculated P y,EYM

AS

172

0.1

nom

inal

cap

acity

0

10000

20000

30000

40000

0 10000 20000 30000 40000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


0

10000

20000

30000

40000

0 10000 20000 30000 40000

Calculated P y,EYM

AS 1

720.

1 no

min

al c

apac

ity

0

10000

20000

30000

40000

0 10000 20000 30000 40000

Calculated P y,EYM

Py,

norm

from

join

t tes

ts


conservative region


with AS1720.1�s nominal capacities (right) for bolts joints loaded perpendicular to grain.

43

Legend: Nominal Capacity EYM’s yield load Py,EYM AS 1720.1 nominal capacityJoint test’s yield load Py,norm

0

500

1000

1500

2000

2500

3000

3500

4000

0 2 4 6 8 10

Displacement (mm)

Load

(N)

Nail N6 A

B

(a)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14

Displacement (mm)

Load

(N)

Nail N9

A

B

A

B

(b)

Figure 4.7 Nailed joints � Comparing experimental data to EYM�s yield load Py,EYM, AS 1720.1�s nominal capacity and joint test�s yield load Py,norm

(a) N6 is a 2-nail joint of (A) 37.5mm and (B) 45mm thick Radiata pine members, and 3.75φ x 75mm long nails.

(b) N9 is a 1-nail joint of 45mm-thick Radiata pine members, and a 3.05φ x 75mm long nail.

44


0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5

Displacement (mm)

Load

(N)

Screw S1A

B

(a)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 10 20 30 40 50

Displaceme nt (mm)

Load

(N)

Screw S3 A

B

(b)

Figure 4.8 Type 17 screw joints � Comparing experimental data to EYM�s yield load Py,EYM, AS 1720.1�s nominal capacity and joint test�s yield load Py,norm

(a) S2 is a 1-screw joint of (A) 18mm and (B) 35mm thick Radiata pine members, and a No. 8 x 40mm long type-17 screw with shank φ = 3.4mm.

(b) S3 is a 1-screw joint of (A) 65mm and (B) 44mm thick Radiata pine members, and a No. 14 x 115mm long type-17 screw with shank φ = 5.2mm.

45


0

1000

2000

3000

4000

5000

6000

0 5 10 15 20 25 30

Displacement (mm)

Load

(N)

Coach Screw CS2 A

B

(a)

0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10 12 14 16

Displaceme nt (m m)

Load

(N)

A

B

Coach Screw CS3

(b)

Figure 4.9 Coach screw joints � Comparing experimental data to EYM�s yield load Py,EYM, AS 1720.1�s nominal capacity and joint test�s yield load Py,norm

(a) CS2 is a 1-coach screw joint of (A) 20mm and (B) 45mm thick Radiata pine members, and 6φ x 65mm long coach screw.

(b) CS3 is a 1-coach screw joint of (A) 35mm and (B) 90mm thick Radiata pine members, and 12φ x 130mm long coach screw.

46


0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25 30

Displaceme nt (mm)

Load

(N)

Bolt BSS1 A

B

(a)

Bolt

0

5000

10000

15000

20000

25000

30000

0 2 4 6 8 10

Displaceme nt (mm)

Load

(N)

Bolt BDS3B

A

(b)

Figure 4.10 Bolted joints parallel to grain � Comparing experimental data to EYM�s yield load Py,EYM, AS 1720.1�s nominal capacity and joint test�s yield load Py,norm

(a) BSS1 is a 1-bolt single shear joint of two 35mm thick Radiata pine members, and an 8φ x 90mm long bolt.

(b) BDS3 is a 1-bolt double shear joint of three Radiata pine members:(A) 35mm, (B) 45mm, (C) 35mm thick, and a 16φ x 130mm long bolt.

47


0

2000

4000

6000

8000

10000

12000

14000

16000

0 2 4 6 8 10 12 14

Displaceme nt (mm)

Load

(N)

Bolt BDS6S

A

B

C

(a)

0

5000

10000

15000

20000

25000

30000

35000

0 2 4 6 8 10 12 14

Displaceme nt (mm)

Load

(N)

A

B

C

Bolt BDS7

(b)

Figure 4.11 Bolted joints perpendicular to grain � Comparing experimental data to EYM�s yield load Py,EYM, AS 1720.1�s nominal capacity and joint test�s yield load Py,norm

(a) BDS6S is a 1-bolt double shear joint of 3 Slash pine members: (A) 35mm, (B) 45mm, and (C) 35mm thick, and an 8φ x 130mm long bolt.

(b) BDS7 is a 1-bolt double shear joint of three Radiata pine members:(A) 35mm, (B) 45mm, and (C) 35mm thick, and a 20φ x 240mm long bolt.

48

5. Concluding Remarks

This document has presented the background details and related technical information

behind the proposed limit-states design procedure for timber joints fabricated using

Australian pine with dowel-type fasteners. The proposed design procedure, presented in

BCE Doc 01/081 (Foliente et al. 2002), is based on the widely accepted European Yield

Model (EYM), providing both consistency and flexibility for the design of joints with dowel-

type fasteners.

The current joint design procedure and design values for dowel-type fasteners in AS 1720.1

have been based on empirical fit of limited Australian data, and the procedures to determine

design values are neither consistent nor fully understood. This means that application of

current design values to new materials used in timber construction may not be appropriate,

and that different safety factors (or levels of reliability) may be obtained from different timber

joints in current design (without the intention of the designer).

The proposed EYM-based design procedure addresses these limitations of the current code.

It has the following features:

• It is based on a comprehensive experimental testing program with matched specimens

for joint testing and component/material testing (i.e., embedment strength and fastener

strength).

• The EYM-based equations of Whale et al. (1987) were selected based on a

comprehensive investigation of various EYM-based equations and comparison with

experimental data.

• The proposed EYM equations have been carefully calibrated to test data.

• The proposed design method allows the use of new components/materials as long as

appropriate properties are known or can be obtained by testing.

• The basis for determining component/material properties and establishing the design

values of joint with dowel-type fasteners is consistent and well documented.

Once implemented, the proposed design procedure would place Australian timber joint

design at par with world�s best practice.

49

References

AF&PA 1997, National design specification for wood construction, NDS-1997, American Forest & Paper Association, Washington, DC.

AF&PA 1999, General dowel equations for calculating lateral connection values, American Forest and Paper Association, Washington DC, USA.

Blass, H.J., Ehlbeck, J. and Rouger, F. 1999, �Simplified design of joints with dowel-type fasteners�, Proceedings of Pacific Timber Engineering Conference (PTEC�99), Forest Research Bulletin 212, New Zealand Forest Research Institute Ltd., Rotorua, New Zealand, Vol. 3: 275-279.

Bryant, A.H. and Hunt, R.D. 1999, �Estimates of joint strength from experimental tests�, Proceedings of Pacific Timber Engineering Conference (PTEC�99), Forest Research Bulletin 212, New Zealand Forest Research Institute Ltd., Rotorua, New Zealand, Vol. 2: 225-230.

Ehlbeck, J. and Larsen, H.J. 1993, �Eurocode 5 � Design of timber structures: joints�, Proceedings of 1992 International Workshop on Wood Connectors, Forest Products Society, Madison , WI, USA, 9-23.

Foliente, G.C. and Leicester, R.H. 1996, �Evaluation of mechanical joint systems in timber structures�, Proceedings of the 25th Forest Products Research Conference, CSIRO Division of Forestry and Forest Products, Clayton, Victoria, Australia, Vol. 1, Paper 2/16, 8 pp.

Foliente, G.C. and Smith, I. 2000, Proposed limit states design method for timber joints − 1. Literature review, CSIRO BCE Doc. 00/039, Highett, Victoria, Australia, 52 pages.

Foliente, G.C. et al. 2002, Proposed limit states design procedure for timber joints with dowel-type fasteners and Australian pine, CSIRO BCE Doc. 01/081, Highett, Victoria, Australia.

Johansen, K W. 1949, Theory of timber connectors, Publication No. 9. International Association of Bridges and Structural Engineering, Bern, Switzerland, 249-262.

Larsen, H.J. 1979, �Design of bolted joints�, Proceedings International Council for Building Research Studies and Documentation: Working Commission W18 - Timber Structures, Bordeaux, France.

MathSoft, 1999, Axum Version 6 � the Industry Standard for Publication-Quality Graphing and Data Analysis Software, MathSoft. Inc, Seatle, WA.

SAA 1995, AS/NZS4291.1. Mechanical Properties of Fasteners − Part 1: Bolts, Screws and Studs. Standards Australia, The Crescent, Homebush, NSW.

SAA 1997, AS 1720.1� 1997. Timber Structures, Part 1: Design methods. Standards Australia, The Crescent, Homebush, NSW.

50

SAA 1998, AS/NZS BBBB (Committee Draft). Timber � Methods for evaluation of mechanical joint systems, Part 1: Static loading; Part 2: Cyclonic wind loading; Part 3: Earthquake loading. Standards Australia, The Crescent, Homebush, NSW.

SAA 2001, AS 1649 � 2001. Timber � Methods of test for mechanical fasteners and connectors � Basic working loads and characteristic strengths. Standards Australia, The Crescent, Homebush, NSW.

SAA 2002, AS 3566.1, Self-drilling screws for the building and construction industries - General requirements and mechanical properties. Standards Australia, The Crescent, Homebush, NSW.

SAA/SNZ 1996a, AS/NZS 1111-1996. ISO Metric Hexagon Commercial Bolts and Screws. Standards Australia, Sydney, NSW.

SAA/SNZ 1996b, AS/NZS 1393-1996. Coach Screws - Metric Series with ISO Hexagon Heads. Standards Australia, Sydney, NSW.

Smith, I. and Foliente, G. 2001, "Limit states design of dowel-fastener joints � Placement of modification factors and partial factors, and calculation of variability in resistance." Proceedings of the 34th CIB-W18 Meeting, Venice, 22-24 August 2001. Published by the University of Karlsruhe, Germany.

Smith, I., Foliente, G.C., Syme, M.J., McNamara, R.I. and Seath, C.A. 2000, Development of limit states design method for timber joints � 2. Comparison of experimental results with EYM predictions, CSIRO BCE Doc 00/177, Highett, Victoria, Australia.

Whale, L.R.J. and Smith, I. 1987, Mechanical timber joints, Research Report 18/86, Timber Research and Development Association, Hughenden Valley, UK.

Whale, L.R.J., Smith, I. and Larsen, H.J. 1987, �Design of nailed and bolted joints - Proposals for the revision of existing formulae in draft Eurocode 5 and the CIB Code�, Proceedings International Council for Building Research Studies and Documentation: Working Commission W18 - Timber Structures, Dublin, Ireland.

51

Appendix A. European Yield Model

Original EYM Model

The following equations describe the original model proposed by Johansen (1949) and

Larsen (1979). Notations are defined in Appendix B.

• 2-Member joints

( ) ( )

( ) ( )

( ) ( )

( )

s

m

2 2 3 2

2

s

22 2

m

2

1.0 II

2 1 1II

1

2 1 4 2III

2

2 1 4 1 2

III2 1

min 4IV

1

y

y H H

y

H

y

H

MP s dl s dl

Ms d l

Ms dl

αβ

β β α α β α β α

β

β β β β β

β

α β β β β βα

β

ββ

+ + + + − +

+ + + + −= +

+ + + − +

+

52

• 3-Member joints

( ) ( )

( )

s

m

2

s

2

1.0 I/ 2 I

2 1 4 2III

2

4IVmin 1

y

Hy H

y

H

Ms dlP s dl

Ms dl

αβ

β β β β β

β

ββ

+ + + −= + +

53

Simplified-1 Equations

Whale et al. (1987) proposed these simplified equations, which include Eqs (2.1) and (2.2)

presented in section 2. These equations are chosen for the development of the LSD

procedure in this project.

Simplified-2 Equations

The proposal by Blass et al. (1999) is given below:

Notations are defined in Appendix B.

PY = sH d l

min

Mode/(Equation)

1 / [1+{(1+β)/β}1/2] interpolation

[{4 βMY}/{sH d l2 (1+ β)}]1/2 IV

α β / [1+{1+β}1/2] interpolation

NOTE: interpolation equations apply when members are too thin to generate a mode IV failure

54

NDS-Screw Model

This model is from the NDS - the US National Design Specification (AF & PA 1997; 1999).

The following equations are written in terms of the EYM notations, which are defined in

Appendix B.

• 2-Member joints

( ) ( ) ( )

s

m

22 2

2 2

s

2 2 2 2 2

m

I

I

11 1 1 12 4

II1 11

2

2 1 1 0.752 4 2 4

III1 1 1

2

2 112 4 2 4

III1 11

2

3.

min

H

H

H

Hy

H

yH

Hy

H

H

s dl

s dl

l l

s d

l l s dl Ms d

Ps d

l l d s dl Ms d

s d

αβ

α α α ββ

β

β

β

α α ββ

β

−+ + − + + +

+

−+ + + +

= +

−+ + + +

+

5 11IV

1 11

y

H

H

Ms d

s d

β

β

+ +

55

Appendix B. NOTATIONS

α = ratio of thickness of main/centre member to thickness of side member

β = ratio of embedment strength of main member to embedment strength of side

member

φ = capacity factor (known as a resistance factor in North America)

d = diameter of fastener

EYM = European Yield Model

l = thickness of side member(s)

= thickness of head-side member in a single-shear nailed joint

LSD = Limit States Design

MY = yield moment of fastener

n = number of fasteners

PY = yield load per fastener per joint plane

Qk = characteristic capacity of a fastener

sH = embedment strength of side member(s)

Notation for EYM-modes:

• Mode I and II correspond to timber bearing failures,

• Modes III and IV correspond to plastic hinge formation in the fastener,

• Subscript �s� means side member yielding,

• Subscript �m� means main member yielding.

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